The invention is based on a sensor as defined hereinafter to the main claim.
Electromagnetic measuring sensors for use as speed sensors in motor vehicles are already known (EP-A-194 213 and EP-A-278 806). The measuring sensors have a two-part housing, in one housing part of which the electrical sensor elements are essentially received. The second housing part is produced by coating the first housing part with plastic; the second housing part fits around the first housing part along the entire circumference of a contact zone between the two housing parts. Since in the region of the contact zone the first housing part has an encompassing collar-like protrusion that is enclosed by the second housing part, not only a force-locking connection but also a form-fitting bond between the two housing parts are attained. Nevertheless, this kind of bond is not moisture-proof over the long term, particularly if the housing is exposed to high alternating temperature stress, vibration, or shear forces from mistakes during assembly.
From the technical dictionary, "ABC Chemie" [ABCs of Chemistry], Verlag Harri Deutsch, Thun and Frankfurt am Main, 1979, it is known to bond like or unlike kinds of materials to one another simply with adhesive, without altering their structure. For example, a melting adhesive that is applied to the solid surface of the workpieces to be bonded must be made liquid by being heated. The setting of the adhesive is brought about by solidification of the melt. Adhesive bonding has thus far not been used in joining housing parts for sensors.
An RPM sensor is already known (German Offenlegungsschrift 34 00 870) in which the first housing part is a coil holder of plastic intended for receiving a pole core, a coil and two current rails. After the completion of the coil holder with the aforementioned electrical components, this holder is received in a second housing part. This part is produced in an injection molding process from plastic and is provided with the embedded end of a line. The housing of the RPM sensor, formed substantially by the two housing parts, also has an opening, which is closed by the insertion of a cap once the line has been connected to the current rails. An RPM sensor of this kind is exposed to severe stress, particularly from moisture, dirt, heat and jarring. The form fit with the second housing part, attained by the fitting in of the first housing part, and the fitting in of the cap still do not protect the RPM sensor reliably against the penetration of moisture, however, which can cause malfunctions or failure. Therefore the two housing parts are additionally materially joined in their contact zone, and the cap is additionally materially joined to the second housing part, by ultrasonic welding. This provision makes the RPM sensor more expensive, because it requires additional assembly steps and considerable expenditure for the apparatus.